The present invention relates to a gas turbine engine, such as those utilized for aircraft applications, which has a system to substantially reduce the formation and emission of nitrogen oxides.
International standards regarding emissions from gas turbine engines, particularly those in aircraft applications, are becoming more stringent, particularly regarding the levels of nitrogen oxides. It is well known that a maximum of nitrogen oxides will be formed in the combustion chamber of a gas turbine engine when the fuel/air mixture in the primary zone of the combustion chamber is near its stoichiometric ratio. At high power operating conditions, such as under full power, the gas temperatures are approximately 2,000.degree. C.
Several proposals have been made in order to reduce the levels of nitrogen oxide emissions from gas turbine engines. U.S. Pat. No. 3,842,597 there to discloses the concept of introducing cooled air into the primary zone for the purpose of lowering the temperature of the combustion gases. The air is introduced through the air swirler enclosing the fuel injector. This system requires components which tap a portion of the air from the gas turbine air compressor, a heat exchanger to cool the tapped air using air from a secondary duct, and means to introduce the flow of tapped and cooled air into the primary zone of the combustion chamber. Such an apparatus is inherently bulky and heavy, thereby increasing the complexity and weight of the gas turbine engine. Also, excessively fuel-rich zones located at the intersection of adjacent fuel injection sprays still produce nitrogen oxide emissions. U.S. Pat. No. 3,705,492 illustrates a gas turbine engine wherein the gases from the turbine pass through a heat exchanger to heat air introduced into the dilution zone of the combustion chamber while the primary air entering through the injector swirlers is unheated in order to reduce the nitrogen oxide emissions. Again, this apparatus requires a heat exchanger and suffers from the weight and complexity penalties imposed by the other known systems.